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Dapol OO Class 122 Bubble Car with DCC Sound

Kit: Zimo MX644D, Zimo Dumbo LS26X20X08-1W, 470uF stay-alive

Dapol seem to be enjoying adding more lighting control to their models these days, but it doesn't always make it easy for DCC installation as many of the commonly-available 21pin DCC decoders do not provide control of every function out-of-the-box. Here we discover one solution which involves a minor rewire and the use of the more common MX644D sound decoder.

The body simply clips off - easiest with finger-nails - nice and simple, but secure clips. Inside is revealed a very neat layout with the 21pin DCC decoder socket hidden beneath a plastic box. Pop the box off and remove the blanking plate.

A quick test on DCC using a standard Zimo MX634D decoder reveals good motor control, and correct lighting control of head/tail lights and the cab lights, which are on independent functions. However, the interior lighting is permanently on, with no way to switch off on DCC. This is to do with not having completely standard MTC-compliant voltages on the higher AUX outputs of these decoders (other supposedly MTC-compliant decoders might work OK, but no guarantee).

The space provided is perfect for a Zimo MX644D sound decoder as shown below.

Remove the 4 screws retaining the seating and an unusual 20mm round speaker enclosure/mount is discovered. This is a very odd choice from Dapol, and I personally wouldn't even consider this size/shape speaker, so we'll look for a better solution!

Instead, solder up a Zimo Dumbo LS26X20X08-1W speaker using the tiny contact pads marked 'LS' - a bit fiddly as the pads are especially small.

To get around the lack of DCC control of the interior lighting, we have to avoid AUX5/FA3 and AUX6/FA4 altogether, and use the next available output from the decoder (AUX7/FA5). This output gives us full power rather than a logic-level output, and avoids going near any circuitry that Dapol might have from the other outputs. Therefore we solder a bridge wire from the AUX7/FA5 pin directly to the output from the interior lighting switch, and ensure that the switch is set to the OFF position so that only the decoder will then control that output.

Add grey and blue wires to the MX644D's stay-alive pads and slot the wires through the hole, replacing the seating.

File a small groove in the decoder cover for the wires to pass through.

Stick the speaker and capacitor on top of the decoder box using something fairly thin as there isn't much vertical spaace available. The capacitor needs to go inner-most as it sits higher - if you put it the other way around then it interferes with one of the cab light switches in the roof lighting strip! Hide the speaker and cap under some black electrical tape to avoid short-circuits and to make it less visible through the windows - it is almost hidden anyway, but not quite through the windows!

Pop the body back on and test that the electrical contacts for the roof circuit are working OK. The decoder will need configuring to have a function key to control AUX7/FA5, but this is straight-forward enough - if you order the decoder from YouChoos, tell us when you order and we can remap it from the start.


Please note that these guides are provided as useful resources for you, as-is. YouChoos cannot be held responsible for errors in the information, or for any damage caused to your models or equipment if you choose to follow any of the steps detailed here.

A bit of YouChoos poster art for your enjoyment!